JPS59153858A - Chromium-nickel-iron alloy having excellent toughness and corrosion resistance - Google Patents

Abstract

PURPOSE:To provide a chromium-nickel-iron alloy having excellent toughness and corrosion resistance by preparing an alloy having the austenite single phase structure consisting of a specific ratio of C, Si, Mn, N, Cr, Fe, Al, Ni and Co. CONSTITUTION:An alloy having the austenite single phase structure consisting, by weight %, of <=0.1% C, <=1% Si, <=1% Mn, <=0.04% N, 20-40% Cr, 10-35% Fe, 0.01-5% Al (part of the whole of Al can be substd. with <=0.15% Ti) and if necessary <=1% Nb + Ta and the balance Ni or Ni and Co and unavoidable impurities is prepd. Co is equivalent with Ni and part or the whole of Ni can be substd. with Co. This alloy provides excellent corrosion resistance under corrosive environment such as heavy oil ash or the ike and the toughness thereof deteriorates less with age under the using condition.

Description

[Detailed Description of the Invention] The present invention provides a material with excellent toughness and corrosion resistance, which has excellent corrosion resistance against corrosion caused by, for example, high-temperature heavy oil ash or coal ash, and has little deterioration of toughness over time under usage conditions. It concerns chromium-nickel-iron alloys.

Structural materials used in heavy oil combustion atmospheres must have excellent corrosion resistance against corrosion caused by high-temperature heavy oil ash, coal ash, etc., and high-temperature strength. Sufficient toughness is now required. In other words, even if structural materials used in heavy oil combustion atmospheres have sufficient toughness before use, their toughness generally deteriorates significantly over time during use. Therefore, there is a strong demand for less deterioration of toughness over time under usage conditions.

Conventionally, materials used under the above-mentioned environment include:
As an austenitic material, 5US304.316
, 321, 347, 310HK40, and ferritic stainless steels include Cyclomaru and 400 series stainless steels.

However, since the austenitic material has a low Cr content, its corrosion resistance is insufficient, and its toughness deteriorates significantly over time. In addition, ferritic stainless steel has better corrosion resistance than the austenitic materials mentioned above, but σ
Toughness is extremely poor due to precipitation of phases.

In addition to the above, Incoloy 800, Incoloy 807,
There are also Ni-based alloys such as Inconel 617, but such Ni-based alloys generally have a large amount of alloying elements, such as Mo,
Since it also contains a considerable amount of elements such as Al and Ti, it has a remarkable tendency to age embrittlement.

The present inventors have conducted intensive research to solve the above-mentioned problems and develop an alloy that has excellent corrosion resistance in corrosive environments such as high-temperature heavy oil ash and coal ash, and has less toughness deterioration over time under usage conditions. As a result, Cr is added to ensure sufficient toughness while maximizing the use of ROM, which is necessary for corrosion resistance.

It was discovered that toughness and corrosion resistance can be improved by adjusting the content of ferrite-forming elements such as Si in the austenite matrix and elements that have a strong tendency to form precipitates such as Mo + Tt + Nb. .

This invention was made based on the above findings, and includes: C: 0.1 wt, % or less.

Si: 1 wt, % or less.

Mn: 1 vit-% or less.

N: 0.04 wt, % or less.

Cr: 20-40wt, %.

Fe: 1 0-35wt, %.

Al: 0.0 1-5 wt, %.

(However, some or all of At may be replaced by T ia O-15
wt.

If necessary, Nb + Ta: 1 wt.% or less.

The remainder: It is characterized by being a chromium-nickel-iron alloy with an austenite-phase structure, which is characterized by its toughness and corrosion resistance, consisting of Nl or Ni and Co and inevitable impurities.

Next, the reason why the composition range of gold of this invention alloy is determined as described above will be explained.

C is an effective element that has the effect of improving high temperature strength. However, a large amount of C is removed during solution treatment.
No melt penetrates into the IJ socks, and even if melt penetrates during solution treatment, most of it is Cr during use at high temperatures.
It precipitates as carbide and impairs toughness. Therefore, in order to prevent the precipitation of such Cr carbides, the C content should be set to 0.1
wt, limited to % or less. Note that the precipitation of Cr carbides is also affected by the addition of Nb, as described later, so if Nb is not included, the C content is reduced to 0.0.
It is preferable to make it 2 wt.% or less.

Si is an element that inevitably enters the alloy because it is used as a deoxidizer, but its content is 1wt.
, % will destabilize the matrix. Therefore, the Si content was limited to 1 wt.% or less.

Mn is an element used together with ClSi as a deoxidizing agent, but if its content exceeds 1 wt, %i, cold workability is impaired. Therefore, the Mn content was limited to 1 wt.% or less.

Cr has the effect of imparting corrosion resistance to heavy oil ash and coal ash. However, if the content is less than 20wt.%, the desired effect described above cannot be obtained, while if the content exceeds 40wt.%, second phases such as α' phase and σ phase will precipitate. As a result, a problem arises in which toughness is impaired. Therefore, the Cr content was limited to a range of 20 to 40 wt%.

Fe has the effect of stabilizing austenite '1.

However, if the content is not within the range of 10 to 35 wt.%, the desired effect described above cannot be obtained, and the use of commercially available scrap and master alloy is attempted.
In addition to not being able to supply cheap fines, 35wt%
Corrosion resistance deteriorates when it exceeds. Therefore, the Fe content was limited to a range of 10 to 35 wt%.

A/= has the effect of fixing O and N that are inevitably mixed in during dissolution. However, if the content is less than 0.01 wt.%, the desired effects described above cannot be obtained, while if the content exceeds 5 wt.%, the austenite becomes unstable. Therefore, the content of At is 0.01 to 5wt.

% within the range.

T1, like At above, has the effect of fixing 0 and N. Therefore, part or all of At can be replaced with Ti. However, in this case, if the Ti content is 0.15 w,t,% or more, large TiN inclusions are formed, leading to a problem of deterioration of toughness.

Therefore, when part or all of At is replaced with Ti, the Ti content should be less than 0.15 wt%.

In the corners and Ta, when the C content is high, such as 0.03 wt.% or more, C and Cr become Cr carbide, which has the effect of preventing the consumption of Cr, which is effective for corrosion resistance. However, when the content exceeds 1 wt.%, the effect becomes saturated and becomes uneconomical. Therefore, the contents of Nb and Ta were limited to 1 wt.% or less.

Furthermore, Ta is equivalent to Nb.

When the content of N exceeds O',04 wt.%, a problem arises in which CrzN is formed and toughness is impaired.

Therefore, the N content was limited to 0.04 wt6% or less.

Elements other than those mentioned above are Ni and Co, excluding unavoidable impurities that are unavoidably contained during melting.

Note that CO is equivalent to Ni, and part or all of Ni can be replaced with k or Co.

Next, the present invention will be explained with reference to examples.

Table 1 shows alloys A-F of the present invention and comparative alloys G-K.

and Charpy impact test results and buanadium corrosion test results after conventional alloy R (which was melted, rolled, subjected to solution treatment, and aged for 200 hours at 700° C.).

The Charpy impact test after aging treatment was conducted for the purpose of investigating the deterioration of toughness over time under usage conditions, and after solution treatment, all sample steels absorbed energy of 30 kq-m or more. Indicated.

In addition, the vanadium corrosion test is 85%V2O5+15
% 100 in NazS04 ash at a temperature of 700°C.
Corrosion loss after immersion in Hr.

As is clear from Table 1, the alloys of the present invention all exhibited toughness of 12 kg-m or more after aging, and the corrosion loss was 1.
0 mglcrl or less, it has excellent toughness and high corrosion resistance.

On the other hand, even if the Cr content is within the range of the present invention, Comparative Alloy G, whose C content is higher than the range of the present invention, has poor toughness even if the corrosion resistance is satisfactory. Comparative alloys H, I, and J whose Cr content is higher than the range of the present invention are α
As a result of the precipitation of the 'Oa and σ phases, the toughness deteriorates significantly even though the corrosion resistance is excellent.

Furthermore, comparative alloys with a Cr content lower than the range of the present invention have extremely poor corrosion resistance even if their toughness is satisfactory.

Note that, like the alloy of the present invention and F, the C content is 0.
．． 0.03 wt.% and 0.05 wt.%.
It is possible to ensure an impact value of -m or more.

In addition, although the conventional alloy Incoloy 800 has a certain level of toughness, it has poor corrosion resistance due to its high lli'e content, and 5US310 is the same (it has poor corrosion resistance and poor toughness due to its high Fe content). .5US304 and 5
Since US316 has a low C'r content and a high Fe content, both have poor corrosion resistance.

Since the alloy of the present invention has the above-mentioned performance,
For example, it has excellent effects when used in heating furnace tubes, hanging fixtures, tile superheaters, etc., and because of its high Cr and Ni content, it can also be used in acid-alkali environments containing chlorine ions. It can exhibit sufficient corrosion resistance.

As described above, the present invention exhibits excellent corrosion resistance in corrosive environments such as high-temperature heavy oil and coal ash, and has industrial advantages such as less deterioration of toughness over time under usage conditions. This will bring about a positive effect.

Applicant: Nippon Kokan Co., Ltd.

Claims (1)

[Claims] (11C: 0.1 wt, % or less. Sl: 1 vit-% or less. Mn: 1 wt, % or less. N: 0.04 wt, % or less. Cr: 20 to 40 wt, %. Fe: 10 to 35 wt, %. At: 0.01 to 5 wt, %. (However, part or all of At can be replaced with 1'i: o, 1 decrease. Less than h) Remaining: N1 or a chromium-nickel-iron alloy with a mastenite-phase structure consisting of Ni and Co and inevitable impurities and excellent toughness and corrosion resistance. (2) c: 0.jwt, % or less pSi: 1
wt, % or less. Mn: 1 wt, % or less. N: 0.04 wt, % or less. Cr: 20-40 wt,%. Fe: 10-35wt, %. At: o, o 1-5wt, %. (However, part or all of A7, T t : 0.15
Wt. (can be substituted with less than 1 wt.) Nb 10 Ta: 1 wt, % or less. Remaining: Ni or chromium-nickel red iron alloy with an austenitic phase structure and excellent toughness and corrosion resistance, consisting of Ni and Co and inevitable impurities.